This invention relates to antennas and more particularly to a broadband electrically small hybrid spiral antenna having a unique profile capable of operation in special volume constrained locations.
Many high performance aircraft have utilized forward looking radars for detection and ranging purposes. The antennae for these radars are usually located in the nose of the aircraft (a prime antenna location) where they are nearest to free space and therefor perform best. With many new aircraft designs there isn't room for the necessary antenna systems in the aircraft nose region. The room problem persists even though various innovative techniques have been devised which allow some systems to be collocated in the aircraft nose or even share a common aperture. Nevertheless, design trade off considerations sometimes dictate that a particular system be put in a less desirable location on the aircraft. For some limited applications, aircraft wing leading edges have been considered.
Frequently, however, the thin wing designs of the aircraft present problems for the antenna designer. For example, for broadband systems, the planar spiral is considered the basic antenna element candidate. This type of element performs well when in an optimum location such as an aircraft nose and provided a relatively blunt radome is used. If, however, a planar spiral antenna element is to be placed in the thin wing, the diameter of the antenna element requires that it be placed a considerable distance aft of the wing's leading edge. This location results in internal radome wall reflections which are a chief cause of degraded performance. Further, the materials used in the wing often are such as to degrade microwave transmission properties. Conventional broadband conical spirals have been investigated as a possible solution and have had only limited success.